1. Field of the Invention
The present invention generally relates to a housing for the distribution of cables, and more particularly to a compact fiber distribution unit which stores excess fiber slack and receives a plurality of fiber optic connectors.
2. Description of the Prior Art
In recent years, fiber optic cables have replaced traditional copper wire as the preferred medium for telecommunications. As with copper wires, it is often necessary to provide cross-connections and interconnections between optical fibers at various locations in the distribution system. The prior art is replete with fiber optic organizers, junction boxes, etc., for this purpose. Several of these inventions utilize fiber organizing trays which slide out of a housing or cabinet-like drawers. In some units, the trays are pivotally attached to the housing. See, e.g., U.S. Pat. Nos. 4,792,203, 4,900,123, 4,911,521, 5,013,121 and 5,093,887.
Common features of a conventional fiber organizing tray include: a spool or reel for storing excess fiber slack and maintaining a minimum bend radius in the fibers to prevent undue stress or kinks; tabs or lugs which keep the fibers from slipping off the reel or out of the tray; a splice area having retaining clips, adhesive, or other means for attaching splice elements to the tray; and a cover for protecting selected portions of the fibers. The cabinets used with these trays sometimes have a movable shelf providing a work surface for, e.g., making the splice connections, and may include a special panel cover or other means for preventing access to certain portions of the cabinet.
It is desirable to maintain the minimum bend radius in all of the stored fibers to avoid microbends which would induce optical losses in the fibers or promote fractures. While the reels of prior art fiber organizing trays provide such a minimum radius for excess fiber slack, many of these tray designs overlook bending of the fiber at other locations. For example, several tray designs include a partition or bulkhead for receiving a plurality of fiber optic connectors. In these designs, the bulkheads are mounted relatively close to a side or front wall of the tray, and the portions of the fibers immediately adjacent the connectors often undergo bending beyond the minimum radius. See, e.g., U.S. Pat. Nos. 4,824,196 (see FIG. 3) and 5,071,211 (see FIG. 23). Although fiber bends must be gentle, this is opposed by requirements to keep fiber optic trays small. Telephone central office racks typically support a 12" maximum component depth, leaving little room for slack storage space in the rear plus room for connectors and couplings in the front area.
This effect is also illustrated in U.S. Pat. No. 4,824,196, which may be the closest prior art. That prior art fiber tray is shown in FIG. 1. Tray 1 generally comprises a base 2 having attached thereto several sheets 3 for separating the slack from several fibers, and a cover 4 hinged to base 1. Cover 4 has several clips 5 for retaining fiber slack. The front wall of base 1 comprises a bulkhead or mounting panel 6 which receives fiber optic connectors 7 of differing formats. A front cover or door 8 is pivotally attached to base 1 adjacent panel 6, door 8 having a front wall 9. As seen in FIG. 1, when door 8 is in its closed, storage position, the portion of fiber 10 leading away from panel 8 undergoes undue bending caused by the proximity of wall 9 to panel 6. In the prior art design of FIG. 1, this effect is somewhat mitigated by the oblique alignment of the connectors 7 with respect to wall 9. Bending of the fibers may also be minimized by extending wall 9 out further from panel 6, but extending wall 9 would be lead to a larger overall tray size, contrary to the highly desired trait of compactness in a fiber distribution unit (FDU). Conversely, panel 6 could be moved further into tray 1, i.e., away from panel 6, without increasing the overall size of the tray, but this would lead to undue bending of the pigtail portion 11 of the fiber against the inner partition 12, which is required to separate the slack storage area (sheets 3) from the connector area (panel 6). These prior art designs consequently have not succeeded in optimizing the spacing of the components and the slack storage areas to the satisfaction of the telecommunications companies which employ them.
Another problem in these types of FDU's relates to the interchangeability of the connector formats used on panel 6. There are several conventional connector formats (variously known as ST, SC, FC, biconic, etc.) all of which are potentially usable in an FDU. Each of these formats, however, typically requires a different style of hole or coupling in the bulkhead for attachment of the connector. Most of these are tedious or difficult to mount in the field, and allow only limited access for individual attention or replacement after being placed in service. Accordingly, FDU's have been designed which provide clips for retaining the connectors, the clips being removably attached in an identical fashion to the FDU front panel or bulkhead regardless of the style of coupling accommodated. Several such prior art designs are illustrated in FIGS. 2A-2C. Each of these designs has significant drawbacks.
In FIG. 2A, the connector clips 13 include integrally molded arrow tines 14 which latch within a tunnel or hood 15 formed in the base 16 of the tray. Clip 13 is very easy to attach, but difficult to remove since it requires two hands performing the separate, but coordinated, actions of pinching the ends of tines 14 toward one another while clip 13 is pulled away from base 16. Access to tines 14 is further impeded by the alignment of the connector 18 with tines 14, i.e., the rearwardly extending portion of connector 18 usually overlies tines 14. Therefore, it is usually necessary to either first remove connector 18, or access tines 14 from underneath base 16.
The connector clip 17 of FIG. 2B employs another simple latching element 18 which catches against a lug 19 formed along the inside wall of a face plate 20. A boss 21 on the underside of clip 17 also catches on another lug. As with the device of FIG. 2A, clip 17 is also easy to install but more difficult to remove. Removal generally requires two hands, one to push down on latching element 18 while the other pushes against the front face of the clip. If two of these clips are stacked in a duplex construction, or two couplings are mounted into a bulkhead permanently affixed to the tray, it is also nearly impossible to access the lower clip unless the upper clip or coupling is first removed.
FIG. 3 depicts another connector clip 22 having flanges 23 which are inserted under a bar 24 formed in the bulkhead or base 25 of the tray, and a latch 26 in the form of a flexural spring which extends through a hole 27 formed in base 25. This design, too, requires the use of two hands to remove, when a connector is installed on the back side of clip 22, since the connector blocks access to latch 26. This requires that one hand release latch 26 from the underside of base 25 while the other hand pulls clip 22 away from the base. Finally, even though latch 26 imparts a spring bias, this design (as well as those of FIGS. 2A and 2B) still does not provide sufficient gripping of the connector clips to the base, resulting in rattling of the clips when jostled. This is undesirable since fiber lines and devices should be protected from motion and mechanical shock whenever possible. It would, therefore, be desirable to devise a connector clip for a fiber organizing tray which is easily installed and removed, without necessitating the prior removal of any connectors attached thereto. This would facilitate access to couplings and connectors stacked in duplex arrangements, and eliminate the problems of field mounting couplings in a bulkhead or separate adapter. The clips would advantageously be attached to the tray in such a manner that they would fit snugly. It would further be desirable and advantageous to provide a construction for a fiber organizing tray which optimizes the spacing of the components and the slack storage areas to enable the tray to maintain a minimum radius for all portions of the fibers, without increasing the overall size of the tray.